Grating spectrographs have been utilized for a number of years to make the absolute measurements of wavelength and to study the structure and intensity of spectral lines of various sources of radiant energy, and have been extremely refined since the earliest experiments by Thomas Young in the early 19th century, which demonstrated the interference effects of light and other radiant energy. At the present time, a conventional high resolution grating spectrograph can measure, for example, the wavelength of a laser to within 0.01 A.degree., however with the absolute calibration only being achieved with the help of spectral lamps and wavelength catalogs, which is, at best, a tedious procedure.
Recently, for determining the absolute wavelength of continuous-wave lasers, interferometers such as described by Kowalski, Hawkins, and Schawlow in the Journal of the Optical Society of America, Vol. 66, 965(1976) have been very effective, but such interferometers do not accommodate themselves to the wavelength measurement of pulsed lasers, which do not permit the easy counting of large numbers of the interferometric fringes.